The study in the Journal of the American Medical Association shows 42 percent of women under 55 do not feel chest pain during a heart attack.
Hospitals often don't diagnose those women properly, until it's too late.
Doctors say there are signs a woman can look out for besides chest pain.
"When women arrive to the hospital having a heart attack with symptoms different than chest pain, their care might not happen as immediate. They might have other symptoms like jaw pain, back pain, shortness of breath, nausea, fatigue and simply sweating," said cardiologist Dr. Suzan Steinbaum.
All of these things could symptoms of a heart attack.
Each year in the U.S. More women die of heart disease than men and heart disease kills more women than all cancers combined.
Doctors say every woman starting at age 20 needs to have her cholesterol and blood pressure checked.